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Tools aid in the transition to NPDS
The turn of the century is a good time to sum up and to determine new trends in glaucoma management. There is no doubt that one of the most progressive directions in glaucoma surgery is non-penetrating filtration surgery. Currently, this technique is known as non-penetrating deep sclerectomy (NPDS).
The first non-penetrating procedure, sinusotomy, was described by M.M. Krasnov in 1964 in Russia. The principle of realization of aqueous humor outflow from the anterior chamber through the unopened trabeculum was further developed by Thomas J. Zimmerman. Sinusotomy and similar techniques may be considered a first generation of non-penetrating glaucoma operations.
A revival of interest in non-penetrating operations and a spread of the technique in Russia and abroad became possible due to the suggestion and experimental substantiation by Valentin Kozlov in 1985 to 1986 of using for outflow the peripheral part of Descemet’s membrane in the projection of Schwalbe’s ring. His clinical intraoperative studies of hydrodynamics proved that after opening Descemet’s membrane, intraocular pressure (IOP) was reduced substantially and the coefficient of the facility of outflow increased, compared with the values after the first stage of the operation – opening of Schlemm’s canal.
This discovery, important from a practical point of view, was the basis of the NPDS suggested in 1987 by Fyodorov and Kozlov. This began a second generation of non-penetrating glaucoma operations.
About the same time, various glaucoma implants also were worked out by Kozlov and co-authors to control postoperative healing. The most popular device in practical application remains a collagen device in the shape of a cigarette filter, which has been applied in Russia for 10 years and is now produced by STAAR Surgical (Monrovia, Calif.) as the Aqua-Flow device.
Various modifications of this method have been described, including the use of viscoelastics and cross-linked hyaluronate, combinations with laser surgery and so on, which increase the surgical options.
However, the technique of NPDS remains relatively complicated, especially at the initial stage of transition from classical trabeculectomy. According to our teaching experience, the technique, using a sharp gem knife under high magnification in denuding thin (50 µm to 70 µm) trabecular-Descemetic plane requires intensive training and high surgical skill. The rate of perforation even among the most experienced surgeons is rather noticeable – 5% to 11%.
Attempts to apply the excimer laser directly to the trabeculum look promising, but a more profound morphological study and a confirmation of the absence of a negative effect on membrane permeability is needed.
Cutting-board technique
Coming back to our training experience, we have observed that the most difficult stages for “beginners” (performing their first hundred operations) are the opening of Schlemm’s canal and the removal of the residual corneal-scleral tissue on the surface of Descemet’s membrane.
This has stimulated us to develop a simplified so-called “cutting-board” technique for NPDS. For surgeons beginning to master the technique, and also to reduce operating time, we have designed a new set of instruments together with Rumex International (Miami), which allows us to minimize contact between sharp cutting edges of knives and the thin trabeculo-Descemetic membrane.
After preparation of the superficial scleral flap and removal of the internal scleral flap according to Kozlov’s technique, we perform only a small opening of the external wall of Schlemm’s canal.
We suggest using a short curved probe with a groove opening Schlemm’s canal (Figure 1). This probe is inserted into the sinus lumen, simultaneously stretching its walls and facilitating further separation. The opening of the external wall of Schlemm’s canal is performed down the groove with a blade, and then the probe is removed. The residual corneal-scleral tissue on the surface of Descemet’s membrane in the zone of Schwalbe’s line is gently separated with a fine micro-spatula without the application of cutting devices (Figure 2).
At the next stage, a specially designed “cutting-board” spatula is inserted between the trabeculum, Descemet’s membrane and the separated corneal layer (Figure 3). Residual layers of sclera and cornea are removed over the cutting-board spatula with a blade (Figure 4) and then the spatula is taken out. It also is possible to perform ablation of the separated corneal-scleral layers on the surface of the cutting-board spatula with laser irradiation.
The surface of Descemet’s membrane is cleaned with a polisher (Figure 5). The working part of this instrument is covered with diamond dust. The criterion of sufficient Descemet’s membrane cleaning is a visible amount of aqueous humor filtration through the membrane.
Easier to perform
The results of application of this method application were studied in 56 eyes with different forms of open-angle glaucoma. Intraoperatively, no cases of perforation were noted. The instruments make the main stage of the procedure easier and more suitable to perform, and reduce the time of surgery.
On the first day after surgery, IOP was 7 mm Hg to 13 mm Hg. In 12 cases, we noted short-term transitional hypotony (up to 3 days) associated with insignificant vision fluctuation (by 0.1). There were no other complications connected with surgery.
It is worth mentioning that within a year of follow-up, only two cases of moderate secondary IOP elevation had taken place, which required YAG-laser Descemeto-goniopuncture. A relatively low rate of YAG-laser goniopucture can be seen as indirect evidence of better functioning of the trabeculo-Descemetic plane. Probably an additional cleaning of the membrane with a polisher can promote better preservation of membrane permeability and more stable filtration.
Greater convenience, prevention of intraoperative perforations and better reproducibility can be considered the advantages of the presented cutting-board technique. The suggested modifications are likely to be useful for surgeons wanting to experience the basic principles of the NPDS method.
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For Your Information:
- Tatiana V. Kozlova, MD, is in the department of glaucoma and high myopia surgery at the Intersectoral Research – Technical Complex Eye Microsurgery. She can be reached by fax at (95) 485-5954; e-mail: t.kozlova@mtu-net.ru. Dr. Kozlova has no direct financial interest in any of the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- For more information on the cutting-board spatula and other instruments described in this article, as well as a video on the technique, contact Rumex International Co. at 10540 N.W. 26th St., Ste. G-203, Miami, FL 33172; (305) 591-2779; fax: (305) 591-2739.